Pheromones for cotton and rice pests

Simple, low cost and non-polluting techniques have been
developed for protecting cotton against three species of bollworm, and for
protecting rice against stem-borer. Plastic strips, impregnated with highly
specific sex-attractant pheromones are distributed within crops. The chemicals,
which mimic the pheromones released by female insects, are slowly released and
so saturate the atmosphere within the crops that males become confused and fail
to locate and mate with the females.

In trials with cotton in Pakistan, plastic twist-ties were used
to release pheromones . Twist-ties consist of a thin wire embedded in plastic:
they are used widely to fasten plastic rubbish bags and are cheap to produce.
For pest control, the plastic is impregnated with the chemical - in this case,
three pheromones specific to pink, spiny and spotted bollworm.

The special twist-ties are attached to the cotton plants before
the pests become established; they provide protection for the critical period of
fruit formation. Immediately before the trial, infestation was so severe that
farmers had to apply pyrethroid every 12 days during fruit formation but with
the use of twist-ties the number of insecticide sprays could be reduced to two

The twist-tie used in cotton was developed by the Shin-Etsu
Chemical Company of Japan. A similar approach has been developed by a British
company, Biological Control Systems, for ricestem borer. BCS produce squares of
black plastic polymer 2 x 2 cm and 1 mm thick, also impregnated with pheromone.
These are placed in split canes, which are distributed in rice fields. Trials in
Spain showed that treatment with pheromones released in this way protected crops
for more than 100 days and gave results comparable to rice fields treated with
conventional pesticide.

The advantage of CTOp protection with pheromones is that they
are not toxic to living organisms and their effect is specific to target
species, leaving Beneficial insects unharmed. However, one problem is that the
intense ultra-violet light in tropical sunshine can inactivate pheromones. Many
insect pheromones occur as isomers, only one of which is active, and uftraviolet
light can induce molecules to <flip> between the two isomeric forms.

Scientists at the University of Wales, Swansea, UK have
developed a way to produce all male Tilapia fish biologically. Until now, this
could be achieved only by treating Tilapia fingerlings with hormones, which can
present problems.

All male Tilapia are necessary for maximum production. If
females are present in a pond males become sexually mature very quickly and are
not worth eating because they are so small. But if it is possible to inhibit
this maturation' the males will put their energy into growth. They are then
ready for the market in a few months

The key to the new technique is gymogenesis, which is the
deveIopment of eggs without fertilization, and which then carry only those genes
derived from the mother. The technique causes male fish, which carry those
genetic factors for producing males, to be converted into females. By
gynogenesis these fish give birth to, and carry only those genes coming from the
mother, which means they will all be male.

The technique that requires a hatchery with the necessary
equipments but such a hatchery could then supply all-male fingerlings to local
fish forms. And this is what scientists from Swansea are now doing in the
Philippines. Trials are now under way with the Bureau of Fisheries and Aquatic
Resources to find a suitable hatchery which will undertake some trials. Local
fish farmers who will join in the trials will then be sought.